Method of making stable invar



Patented Aug. 11, 1936 PATENT OFFICE METHOD OF MAKING STABLE INVARHoward Scott, Forest Hills, Pa., assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania No Drawing. Application March 15, 1934, Serial.No. 715,660

10 Claims.

This invention relates to alloys of high purity and especially tolow-expansion alloys of iron and nickel having exceptional ductility andhot-working properties, and to a process of making the same.

In certain uses of Invar metal, it is desirable to employ a metal ofhigh stability, that is, a metal which will not change its physicaldimensions while in service. For example, the precision of base lines insurveys is severely restricted by the instability of most Invar tapesavailable for use. One cause of this instability is the presence ofimpurities of-low solubility, such as nitrogen, oxygen, carbon andsulphur, in the metal from which the tape is made. Stable Invar can beobtained by producing a high purity alloy of iron and nickel with orwithout cobalt as one of the composition metals.

According to the present invention, low-expansion alloys of iron andnickel of exceptional purity having a low oxide and non-metallicinclusion content and a low sulphur content (that is, below 0.01%) andcharacterized by exceptionally good ductility and hot-working propertiesare produced. I have. found that such a stable Invar may be prepared byfirst purifying the major component metals by heating the separatemetals in the solid state, but at a temperature of above 1000 C., in anatmosphere of hydrogen gas from ten to forty-eight hours, and thencompounding by melting the metals and alloying them in a molded stateunder conditions which prevent the material from oxidizing.

Electrolytic iron and nickel may be used to advantage since electrolysisremoves elements of high solid solubility and particularly those thatare harmful to the expansion properties of the metals. This is notessential, however, since good results can be obtained with other iron,nickel, and cobalt of a relatively high degree of purity such, forexample, as those prepared by the carbonyl process. The metals should bein a finely divided state or in porous condition, as whenelectro-deposited, and are purified in the solid state by annealing inhyrogen gas at 1000 C, to 1300.

C. for at least ten hours prior to melting and casting. I have foundthat heating at 1150 C. for twenty hours is quite effective; Thistreatment practically eliminates all the undesirable residual elementssuch as carbon, oxygen, nitrogen and sulphur from the electrolyticallydeposited base metal.

The iron and nickel so purified are melted together, preferably in aninduction furnace, in an atmosphere of hydrogen, and solidified in thesame atmosphere to avoid taking up oxygen. As a result, the solid metalis porous near the surface where. there are blow holes caused byescaping gases but this is not injurious to the metal because, in theabsence of oxides, the blow holes weld shut completely upon forging ofthe material.

Instead of melting and freezing the alloyed material under hydrogenafter purification in the solid state, an alternate method of treatmentmay be employed. It the component metals have been annealed in anatmosphere of hydrogen, they may be then melted together in contact withair, preferably putting a slag on the metal vwhen in a molten condition,and deoxidizing in the usual way with silicon, manganese, or aluminum,or any combination of these or other deoxidizing elements, after whichthe molten metal is poured into a mold. Alloys so prepared can be forgedand fabricated with ease, chiefly because the sulphur content is low.The sulphur content provides a practical index of the purity of thealloy, and with the above-described process, is ordinarily below 0.01%.

A typical composition of Invar produced by the above-described methodis: 36.85% nickel plus cobalt, 0.000% manganese, 0.011% silicon, 0.003%sulphur, 0.008% phosphorous, copper nil, the remainder of the materialbeing iron. This process is equally applicable to other alloys wherehigh purity is essential, such as iron, nickeland cobalt alloys, forsealing into hard glass and ferro-alloys for the deoxidatlon of steel.

I claim as my invention: Y

1. The method of preparing, alloys of iron and nickel which consists inannealing electrolytic iron and nickel and other high purity products inan atmosphere of hydrogen gas at a temperature of about 1150 C. fortwenty hours and thenmelting and freezing in an atmosphere of purehydrogen.

2. The method of preparing a low-expansion alloy of iron, nickel andcobalt which consists in heating high purity components in anatmosphereof hydrogen gas at a temperature of between 1000 and 1300? C. for atleast ten hours, and then melting and freezing in an atmosphere of purehydrogen.

3. The method of preparing a low-expansion alloy of iron and nickelwhich consists in heating high purity components in an atmosphere ofhydrogen gas at a temperature of between 1000 and 1300 C. for ten toforty-eight hours and in compounding by alloying and deoxidizing in themolten state.

4. The process of producing a non-porous stable Invar nickel iron alloycharacterized by exceptionally good ductility and hot workingproperties, and a sulphur content below 0.01 per cent, which consists inannealing the component metals in an atmosphere of hydrogen gas at atemperature between 1000 and'130il" C. for at least ten hours andthereafter compounding the metals by melting. v

5. The process of producing a stable Invar alloy of iron and nickelcharacterized by exceptionally good ductility and hot working propertiesand sulphur content below om per cent which consists, in purifying inthe solid state by annealing in hydrogen gas at between 1000 and 1 300C. for at least ten hoursand thereafter melting and further deoxidingthe metal.

6. The process of producing a stable Invar al- 10y of iron and nickelwhich consists in purifying in the solid state by annealing in hydrogengas at a temperature between 1000 and 1300 C. for from ten toforty-eight hours, and thereafter further deoxidizing the material inthe molten state.

7. The process of producing a non-porous stable Invar alloy of iron andnickel having a purity of 99.90 per cent or better and having low oxideand non-metallic inclusion content, which consists in purifying themajor components in the solid state by annealing in hydrogen gas at atemperature over 1000 C. and in compounding by alloying in the moltenstate.

8. In the process of making iron-nickel alloys, the steps of heattreating iron in a finely divided solid state in a hydrogen atmosphereto produce a pure base metal, mixing the iron with the nickel andmelting the mixed metals to compound them 10 into an alloy.

9. In the process of making iron-nickel-cobalt alloys, the steps of heattreating iron, nickel and cobalt in a finely divided state in a hydrogenatmosphere to produce pure metals, mixing the 15 iron with the nickeland cobalt and melting the mixed metals to compound them into an alloy.

10. In the process of making iron, nickel and/or cobalt alloys the stepsof heat treating the iron, nickel and/or cobalt in a finely dividedsolid state 20 at temperatures above 1000 C. in a hydrogen atmosphere toproduce pure metals, mixing the iron with the nickel and/or cobalt andmelting the purified mixed metals to compound them into an alloy. 25

HOWARD SCOTT.

